1. Field of the Invention
This invention relates to a CNC machine tool, more particularly to a center frame of a CNC machine tool.
2. Description of the Related Art
FIG. 1 illustrates a center frame 10 of a CNC machine tool 1 as disclosed in Taiwanese Patent No. M462163. To conduct machining of a long workpiece 8 on the machine tool 1, the center frame 10 is used for clamping the workpiece 8 in order to prevent flexing of the workpiece 8 due to excessive length thereof, so that an accurate machining of the workpiece 8 can be performed. The center frame 10 mainly includes a base 11 mounted on the machine tool 1, a pair of clamps 12 respectively pivoted to upper and lower portions of the base 11, a pair of drive units 13 mounted on the base 11 and respectively driving rotations of the clamps 12 relative to the base 11, and a central abutment support unit 14 mounted on the base 11 between the clamps 12. The clamps 12 are driven by the drive units 13 to abut against or to move away from the workpiece 8. The central abutment support unit 14 includes an operating portion 141 connected to the base 11, and an abutment portion 142 for abutting against the workpiece 8. The operating portion 141 is operated to move the abutment portion 142 to abut against or away from the workpiece 8. The center frame 10 utilizes coordination between the base 11 and the clamps 12, the drive units 13 and the central abutment support unit 14 for stably supporting the workpiece 8.
Because the drive units 13 and the clamps 12 are linked through a screwed structure, when the drive units 13 are operated to drive the clamps 12 to abut against or away from the workpiece 8, the movements of the clamps 12 are slow, so that clamping or removal time of the workpiece 8 is lengthened. Furthermore, because the angle of rotation of the clamps 12 toward or away from each other is limited, the workpiece 8 can only be moved in or out of the center frame 10 through an opening between the clamps 12.